1. Field of the Invention
The present invention relates, in general, to a sewage treatment apparatus for purifying wastewater such as sewage and, more particularly, to a high efficiency apparatus for treating nitrogen and phosphorus contained in sewage in case of very low concentration of substrate contained in influent.
2. Description of the Prior Art
In a conventional sewage treatment apparatus, it is impossible to obtain a condition suitable for sewage treatment when sewage in low in concentration or temperature. As a result, loss of sludge occurs in an anaerobic tank equipped in such a conventional sewage treatment apparatus. In addition, the conventional sewage treatment apparatus is typically configured to directly introduce wastewater into the anaerobic tank. However, this configuration accelerates the sludge wash-out in the anaerobic tank, which lowers the removal efficiency of nitrogen and phosphorus.